@ScottNZ 

The visibility of infrared light to the human eye isn't the reason for the reflections seen in the camera's image when it is placed behind glass. Infrared light consists of various wavelengths, some of which are invisible to us (e.g. 940 nm IR LED). However, infrared LEDs continue to emit this light. Consequently, when the camera is positioned behind a glass window, the infrared light is reflected, which can impact the quality of the camera's image.